A coolant thermoelectric generation system may include a thermoelectric module 20 connected to a high temperature line 13 through which engine coolant flows and a low temperature line 24 through which coolant having a temperature lower than a temperature of the engine coolant flows, and configured to perform thermoelectric generation with a heat exchange effect based on a coolant temperature difference between the engine coolant and the coolant having a temperature lower than a temperature of the engine coolant with a thermoelectric element 21 interposed therebetween; a heat exchange line 16, in which the heat exchange effect occurs, and a bypass line 17, in which no heat exchange effect occurs, the heat exchange line and the bypass line connected to the high temperature line to form two paths, respectively 13; and built-in valves 14, 14-1, 14-2 located in the internal space of the thermoelectric module, and configured to adjust flow rates of the coolant in the heat exchange line and the bypass line.